Field of the Invention. Embodiments of invention relate to hearing aids. More specifically embodiments of the invention relate to protective caps for improving the resistance of hearings to exposure from cerumen and other biological contaminants.
Since many hearing aid devices are adapted to be fit into the ear canal, a brief description of the anatomy of the ear canal will now be presented for purposes of illustration. While, the shape and structure, or morphology, of the ear canal can vary from person to person, certain characteristics are common to all individuals. Referring now to FIGS. 1-2, the external acoustic meatus (ear canal) is generally narrow and contoured as shown in the coronal view in FIG. 1. The ear canal 10 is approximately 25 mm in length from the canal aperture 17 to the center of the tympanic membrane 18 (eardrum). The lateral part (away from the tympanic membrane) of the ear canal, a cartilaginous region 11, is relatively soft due to the underlying cartilaginous tissue. The cartilaginous region 11 of the ear canal 10 deforms and moves in response to the mandibular (jaw) motions, which occur during talking, yawning, eating, etc. The medial (towards the tympanic membrane) part, a bony region 13 proximal to the tympanic membrane, is rigid due to the underlying bony tissue. The skin 14 in the bony region 13 is thin (relative to the skin 16 in the cartilaginous region) and is more sensitive to touch or pressure. There is a characteristic bend 15 that roughly occurs at the bony-cartilaginous junction 19 (referred to herein as the bony junction), which separates the cartilaginous 11 and the bony 13 regions. The magnitude of this bend varies among individuals.
A cross-sectional view of the typical ear canal 10 (FIG. 2) reveals generally an oval shape and pointed inferiorly (lower side). The long diameter (DL) is along the vertical axis and the short diameter (DS) is along the horizontal axis. These dimensions vary among individuals.
Hair 5 and debris 4 in the ear canal are primarily present in the cartilaginous region 11. Physiologic debris includes cerumen (earwax), sweat, decayed hair, and oils produced by the various glands underneath the skin in the cartilaginous region. Non-physiologic debris consists primarily of environmental particles that enter the ear canal. Canal debris is naturally extruded to the outside of the ear by the process of lateral epithelial cell migration (see e.g., Ballachanda, The Human ear Canal, Singular Publishing, 1995, pp. 195). There is no cerumen production or hair in the bony part of the ear canal.
The ear canal 10 terminates medially with the tympanic membrane 18. Laterally and external to the ear canal is the concha cavity 2 and the auricle 3, both also cartilaginous. The junction between the concha cavity 2 and the cartilaginous part 11 of the ear canal at the aperture 17 is also defined by a characteristic bend 12 known as the first bend of the ear canal.
First generation hearing devices were primarily of the Behind-The-Ear (BTE) type. However, they have been largely replaced by In-The-Canal (ITC) hearing devices are of which there are three types. In-The-Ear (ITE) devices rest primarily in the concha of the ear and have the disadvantages of being fairly conspicuous to a bystander and relatively bulky to wear. Smaller In-The-Canal (ITC) devices fit partially in the concha and partially in the ear canal and are less visible but still leave a substantial portion of the hearing device exposed. Recently, Completely-In-The-Canal (CIC) hearing devices have come into greater use. These devices fit deep within the ear canal and can be essentially hidden from view from the outside.
In addition to the obvious cosmetic advantages, CIC hearing devices provide, they also have several performance advantages that larger, externally mounted devices do not offer. Placing the hearing device deep within the ear canal and proximate to the tympanic membrane (ear drum) improves the frequency response of the device, reduces distortion due to jaw extrusion, reduces the occurrence of the occlusion effect and improves overall sound fidelity.
However despite their advantages, many CIC hearing devices have performance and reliability issues relating to occlusion effects and the exposure of their components to moisture, cerumen, perspiration and other contaminants entering the ear canal (e.g. soap, pool water, etc.). Attempts have been made to use filters to protect components such as the sound ports of the microphone. However over time, the filters can become clogged with cerumen, and other contamination. Other attempts have been made to seal the entire hearing aid to prevent in the influx of mixture and cerumen; however, such seals can be difficult to both reliably form and test as wells as reducing acoustic conductance to the hearing aid microphone. Also many seals can fail over time due to the high humidity environment in the ear canal resulting in liquid water or vapor entering and becoming trapped inside the hearing aid and then condensing. Accordingly, there is a need for improved moisture and cerumen protection methodologies for CIC hearing aid components.